Known ABS resins, which have excellent heat resistance, impact resistance, molding-processability and surface gloss have been widely used as a material for industrial parts. For example, these resins have been used in the internal and/or external parts of automobiles, toys, office devices, and so forth. Known methods for preparing ABS resin are emulsion polymerization and bulk continuous polymerization.
However, there are situations where a low-gloss surface is desired. For example, where ABS resin is to be used for the internal parts of automobiles, a low-gloss surface is required to prevent problems in which the driver's field of vision is obstructed due to surface gloss.
Known methods for preparing a low-gloss resins include methods wherein the resin surface is embossed or provided with a low-gloss coating. Moreover, Japanese Unexamined Patent Publication No. 60-44517 discloses a method for reducing compatibility between the phases used or for using a polybutadiene latex of large particle size during the process for preparing the ABS resin. In addition, Japanese Unexamined Patent Publication No. 59-89346 discloses low-gloss ABS resins that include olefin copolymers having epoxy groups. Finally, Korean Patent Publication No. 93-6912 discloses a method of achieving low-gloss properties by finishing bulk polymerization before stabilizing the rubber particles so that after phase inversion, the rubber particles do not have spherical shapes but rather are split.
However, the above embossing method is problematic in that the gloss on resin surface is strongly influenced by the molding conditions. And the above low-gloss coating method, while providing a low-gloss resin, results in molded products that have poor mechanical properties at high cost.
Japanese Unexamined Patent Publication No. 60-44517 has the following problems: (1) the gloss level is not uniform and varies according to the additives used and the injection conditions; (2) control of the reaction time is difficult during polymerization; and (3) the mechanical properties such as impact strength and so forth are greatly decreased, because the composition contains excessive non-grafted rubber particles in the ABS resin compositions.
Japanese Unexamined Patent Publication No. 59-89346 has problems associated with control of the gloss level. Control of the gloss level is difficult because the gloss level is highly sensitive to changes in the mixing ratio of copolymers having epoxy groups. Moreover, in cases of molding at high temperatures, gloss may be increased, while impact strength and fluidity are decreased due to low compatibility between the constituent resins.
Finally, Korean Patent Publication No. 93-6912 has the following problems: (1) due to early completion of bulk polymerization before phase inversion, less monomer-occluded rubber particles are formed, and impact strength is thus decreased; and (2) since the obtained products have the same heat resistance as general ABS resins, they may not be used for products requiring higher heat resistance such as the internal parts of automobiles.
In conducting research to solve the above problems, the inventors unexpectedly discovered that impact resistant ABS resins having excellent low-gloss properties, heat resistance and mechanical properties can be prepared in accordance with a bulk/suspension polymerization process wherein the conditions and the extent of polymerization are controlled in each reaction step to form rubber particles of defined size and shape.